Yeast in aqueous suspension, when it is stored under favorable conditions, has indisputable advantages compared with yeasts in solid form, so-called pressed or dried yeast, in particular because of its simplified use, the fact that it is pre-dosed, and its good performance levels which, moreover, make it a product that is appreciated by those working in the bakery trade. As it happens, yeast in aqueous suspension is a product that is very sensitive to its storage conditions, in particular its environment (temperature, pH, CO2/O2 content, etc.), and particularly exposed to contaminations. It is thus a product difficult to package which thus requires hygienic storage conditions which at the same time make it possible to maintain its microbiological quality, its performance levels, in particular in terms of fermenting capacity, and its organoleptic qualities. In addition, the activity and the reactivity of a yeast, while they are responsible for good performance levels during its use, constitute a drawback specific to the storage of such a product. For good storage of the yeast, it is therefore desirable in practice to maintain said yeast in aqueous suspension at low temperature, of about 4° C., and to provide for specific degassing means, in particular for the release of the gases resulting from the yeast respiration metabolism, in particular carbon dioxide, while at the same time limiting the other gas exchanges (oxygen from the ambient air) in particular in order to avoid the development of contaminations.
Several solutions for packaging yeast in aqueous suspension have been proposed. One of these solutions consists in packaging the liquid yeast in a Bag-in-Box. The principle of the Bag-in-Box is to have, in a box generally made of cardboard (see, for example, American U.S. Pat. No. 6,223,981), a flexible bag which has one or more filling and/or emptying orifices, called bases (see, for example, American U.S. Pat. No. 4,863,770). Each base may have a screw thread or rings making it possible, respectively, to screw on or clip on a cap. The Bag-in-Box thus formed may be stored, for several weeks, at a temperature of between 0 and 6° C. and at a relative humidity of between 50% and 100%. The user may recover a given amount of yeast in aqueous suspension thus stored using a valve or a tap attached to a base after having removed the cap. In the case where a valve is put in place, the user turns the Bag-in-Box completely upside down and places it in an appropriate refrigerated dispenser (see, for example, the system described by the present applicant in international application WO 2004/048253). In the case where a tap is put in place, the Bag-in-Box is placed in the horizontal position in a refrigerator or a cold room.
In order to avoid swelling of the flexible bag contained in the carton of the Bag-in-Box under the action of the carbon dioxide produced by the yeast, orifices forming vents are provided for as specific degassing means (see, for example, European patent EP 0 792 930-B1 and international application WO 2004/048253 from the Applicant). Furthermore, the flexible bag is proportioned so as to leave a sufficient headspace in the Bag-in-Box to allow the gas to be stored until a sufficient pressure allowing evacuation of the gas through the degasser cap is reached. However, this degassing system is not entirely satisfactory, in particular when the liquid yeast stored is a non-stabilized yeast which produces larger amounts of CO2 than stabilized yeast. Indeed, the swelling of the flexible bag, which may cause a deformation of the carton, giving it a bulging appearance, creates not only problems of stability of the Bag-in-Box, but may also prevent its insertion into the refrigerated dispenser. In certain cases, the swelling can lead to rupture of the carton. Furthermore, if the Bag-in-Box is under pressure, the opening thereof by the user may produce a geyser of product. Finally, when a Bag-in-Box is transported or handled, if the yeast comes into contact with the degasser cap, the latter may be momentarily or permanently clogged.
Application EP 2 019 051 by the present Applicant describes a packaging for a liquid product containing yeast comprising a permeable material which has an S/M ratio (exchange surface area S of the material expressed in cm2 relative to the mass M of the liquid product containing yeast expressed in grams), and coefficients of oxygen (O2) permeability and of carbon dioxide (CO2) permeability determined so as, in particular, to avoid swelling of the product and to prevent the penetration of contaminants. However, such an S/M ratio does not allow much freedom regarding the choice of the shape and the dimensions of the pouch.
Therefore, there is a need for packagings which are suitable for the storage and maintaining of liquid products containing yeast and which allow better degassing of the CO2 produced by yeast respiratory metabolism.